Home Man
Today's Posts

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:
Select Section of Man Page:
Select Man Page Repository:

CentOS 7.0 - man page for faxformat (centos section 1)

Fax Formats(1)									   Fax Formats(1)

       This  page, part of the Netpbmuser'sguide(1) , describes FAX formats in relation to Netpbm

       The ITU (formerly CCITT) publishes standards for operation of fax machines (the idea is to
       provide	a  way	to  be sure that a fax machine is able to receive a fax sent by another).
       These standards incidentally specify graphics file formats -- a protocol for  representing
       a visual image in sequences of bits.

       The  two  relevant  standards are called Group 3 (G3) and Group 4 (G4) (Groups 1 and 2 are
       analog standards no longer in use).  Virtually every fax machine in existence conforms  at
       least generally to at least one of these standards.

       The  standard  for Group 3 fax is defined in ITU Recommendation T.4.  In the U.S., that is
       implemented by EIA standards EIA-465 and EIA-466.  These standards  cover  more	than  the
       file  format  as well, including how to transmit bits over a telephone line and procedures
       for handling document transmissions.

       G3 faxes are 204 dots per inch (dpi) horizontally and 98 dpi (196 dpi optionally, in fine-
       detail mode) vertically.

       The  standards  specify	three  file  formats  (also called coding methods and compression
       schemes -- remember the standard doesn't mention computer files; it talks about the format
       of a stream of bits travelling over a telephone line):

       MH     This  compresses	in one dimension: it compresses individual raster lines but makes
	      no attempt to compress redundancy between lines.

	      One dimensional compression is traditionally the best a fax  machine  could  handle
	      because  G3  neither  assumes  error  free transmission not retransmits when errors
	      occur, and receiving fax machines traditionally could not afford to buffer much  of
	      a  page.	 It's  important that when there is an error in a raster line, its impact
	      not spread to many lines after it.

	      All Group 3 and Group 4 fax machines must be able to send and receive MH.

	      MH is sometimes called 'G3,' but that is a poor name  because  while  the  Group	3
	      standard does specify MH, it has always specified other formats too.

	      MH  is  sometimes  called 'T4' based on the name of the document that specifies it,
	      ITU T.4.	But this is a poor name because T.4 also specifies MR.

       MR     This compresses in two dimensions, horizontally and vertically.

	      MR has always been part of the Group 3 standard, but is optional	(a  Group  3  fax
	      machine may or may not be able to send and receive it).

       MMR    This  is	a  more advanced format than the others.  It is even more two-dimensional
	      than MR.	It is optional in the Group 3 standard, and didn't even exist in  earlier
	      versions	of  it.  It was developed specifically for the Group 4 standard, but then
	      added to an extended Group 3 standard as well.

	      MMR is sometimes called Group 4, but that is a poor name because of the  fact  that
	      it is also part of the current Group 3 standard.

	      MMR is sometimes called 'T6' based on the name of the document
	       that specifies it, ITU T.6.

       g3topbm converts the MH format to PBM.  pbmtog3 converts PBM to MH.

       There is no Netpbm program to convert to or from other fax formats.

       The  TIFF  format is flexible enough to allow lots of different coding methods, within it.
       There are TIFF subformats for MH, MR, and MMR, among others.  These are particularly  use-
       ful when you receive a fax as a TIFF file.

       tifftopnm recognizes and can convert from any of these.

       pamtotiff can convert to any of these; you use command options to choose which.

netpbm documentation			 03 December 2008			   Fax Formats(1)

All times are GMT -4. The time now is 10:26 AM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
Show Password

Not a Forum Member?
Forgot Password?